Study on the technology of permeability enhancement of deep hole pre-splitting blasting in a low-permeability coal seam

In order to increase the permeability of low permeability and high gas coal seam and improve the efficiency and utilization of gas extraction, the permeability enhancement technology of deep hole pre-splitting blasting is proposed, and the mechanism of blasting induced cracking of deep hole pre-splitting blasting is analyzed. ANSYS/LS-DYNA is used to simulate the propagation law of blasting stress wave and crack propagation under different process parameters. At the same time, the field industrial test was carried out on the 16,071 working face of Jiulishan Mine, in order to verify the effect of gas drainage and permeability improvement after deep hole pre-splitting blasting technology for low permeability and high gas seam. The results show that with the decrease of the decoupling coefficient, the number and density of cracks in the fracture zone gradually increase, and the number of coal failure units obviously increases. However, the increase range of the number and density of fringes in the fracture zone weakens when the value exceeds a certain value. By setting control holes, cracks can be formed through blasting holes and control holes to promote the expansion of cracks in the coal body, and then improve the permeability of the coal seam. When the distance between the blasting hole and the control hole is set to 3 m, the permeability improvement is the most ideal. Compared with natural extraction, the limit gas extraction amount of drilling hole after deep hole pre-splitting blasting is 3.71 times that of ordinary drilling hole. The results of numerical simulation and industrial field tests prove that the proposed deep hole pre-cracking blasting can effectively increase the permeability of low permeability coal strata, improve the gas extraction rate, and reduce gas disasters, which provides theoretical reference and field guidance for other low permeability coal seam.